1. Field of the Invention
This invention relates to an apparatus and method for aligning and fixing a ribbon on a solar cell in order to facilitate forming a solar panel typically comprising several solar cells. In particular, the invention is related to such an apparatus and method, wherein the ribbon is a pre-tinned metal ribbon. Furthermore, the invention is related to a solar cell on which an above-mentioned ribbon is fixed.
2. Related Art
In the Photovoltaic industry, crystalline solar panels are made by interconnecting individual solar cells together in a line to form a complete circuit. The back of one cell is electrically connected to the front of the next. This process, known as stringing, is used to connect each row of the matrix known as a solar module. The interconnection is accomplished through the use of thin and flat strips of pre-tinned copper ribbon. The ribbon must be accurately aligned with a pre-printed stripe (bus bar) on the front of the cell. Misalignment of the ribbon relative to the bus bar causes power output losses and is not aesthetically pleasing. Therefore, ribbon alignment on the front of the solar cell is of great importance and has been a difficult challenge for many machines to accomplish. The difficulty is typically associated with the “flimsy” nature of the ribbon in its free state as well as camber problems with ribbon.
A general concept for aligning and fixing such a ribbon is disclosed in U.S. 2003/0127124 A1 which document is incorporated by reference here within in order to enable the skilled person being introduced in the technique.
In JP 2004-111464 A and in JP 2000-022188 A further background for the skilled person is disclosed.
Two general concepts exist on current Stringing machines from other suppliers.
The first concept holds the leading end of the ribbon(s), pulls it to length, cuts it, and moves it to position over the cells. With this approach, control of the trailing end of the ribbon is lost as soon as the ribbon is cut. If camber exists in the ribbon (which is common) then the alignment between the ribbon and the cell suffers.
The second concept grips both ends of the ribbon even after it is cut, but then lays the ribbon in a groove. A second “vacuum gripper” picks the ribbon from above and carries it to the cell(s). With this approach, picking ribbon with vacuum can be a problem and camber is also a problem. To avoid the camber problem, this company “stretches” the ribbon into yield before placing into the groove. This causes work hardening of the ribbon which has been linked to crystal damage of the cells after soldering.